slo shales from Sobniow only very few detached scales of the genus 

 Clupea. 



The following 5 types of manner of preservation have been distin- 

 guished in the material considered here: 



(1) undeformed straight skeletons (Plates II, III) constitute 67.8 

 percent of the entire material — 3^.8 percent of that figure belong to 

 the Myctophidae, 26.2 percent to the Sternoptychidae, 4.5. percent to 

 the Gonostomidae; 



(2) forms slightly curved (Plate I, Fig. 1) constitute 20.1 percent, 

 (Myctophidae 13.3, Gonostomidae 5.7, Clupeidae 1.1 percent); 



(3) forms displaying stronger deformations (Plate V) constitute 3.6 

 percent (Sternoptychidae 0.3, Gonostomidae 1.9 percent); 



(4) detached skulls (Plate VI) constitute 7.5 percent (Sternopty- 

 chidae 2.6, Clupeidae 4.9 percent); 



(5) one headless bodytrunk = 0.9 percent. 



The presence in the Jaslo shales of various conditions of preser- 

 vation agrees with the information on other fossil ichthyofaunas pres- 

 ented by numerous authors; according to these suggestions, the following 

 interpretation may be advanced for each of the groups mentioned 

 above. 



Group 1. Deformation is completely lacking in most representa- 

 tives of the Sternoptychidae — fishes of a considerable body-depth. This 

 confirms Weiler's (1929) opinion that the post-morten bending of the 

 axial skeleton usually occurs only in fishes with a low body-depth. By 

 contrast, in fishes with a deep flattened body, the bending does not 

 occur at all, or to a very small degree. 



Group 2. Slight body deformations, expressed by gently arched cur- 

 vature, occur in the Myctophidae, partly also the Gonostomidae and 

 Clupeidae. In the last named this phenomenon is fairly frequent, being 

 probably due to post-mortem contraction of muscles. An interesting 

 experiment was carried out by Weiler (1929) concerning the post-mor- 

 tem behavior of the living forms from genus Clupea L. He noted that 

 in these fishes deformations follow very soon after death; within 1 — IV2 

 days, the head and the forebody bend upwards, within 2 — 3 days the 

 curvature of the body reaches its maximum, and the abdomen bursts 

 open behind the pectoral fins. If the process of decay is not stopped, 

 the head breaks off, frequently with some portion of the body trunk 

 attached to it. 



Group 3. Two causes for the body deformations may reasonably 

 be suggested here: 



(a) either natural post-mortem bending, magnified by water cur- 

 rent, results in the mutually parallel position of the fore and back 



41 



